If you have a good moveset for Slurpuff, post an answer below and upvote the best ones. Remember, this is for competitive movesets, not in-game. Ability, EVs etc should be included. Make sure to read all the guidelines here.

I love Slurpuff. My second favorite Pokemon ever. I have two of them, but I will post my physical sweeper.
Slurpuff: Cotton Candy Physical Knight
Ability: Unburden
Item: Sitrus Berry

Wish
Belly Drum
Play Rough
Hidden Power(Ground)
This set works greatly. First thing you want to do is use Wish before anything. On the next turn, use Belly Drum. The Sitrus Berry will restore a bit of your health, while Wish will heal the rest. With the berry gone, your speed will double thanks to its ability. With maximized attack, sweep with Play Rough. If you come across a Poison, Steel, or Fire type, which, correct me if I'm wrong, are the only types to resist Fairy type moves. Crush them with Hidden Power Ground. Hidden Power also helps if you happen to come across a physical wall.
Hope this helped!

Now that ORAS is out, and with it, new move tutor moves, Slurpuff will wreak havoc due to only one move it gets: Drain Punch.
Now it will no longer be walled by Steel- and Fire-types, unless they're the Honedge line or the Litwick line. Of course, Poison-types prove a massive problem, so it's a good idea to get rid of all the opposing Poison-types before bringing Slurpuff in to sweep.

Really not sure what this guy is supposed to be.
An dessert-puff-thingy with all round stats all around base 80. So like Phione? :D?
Slurpuff @ Leftovers
EVs: 252 HP / 252 Def / 4 S.Def
Trait: Sweet Veil
Bold Nature
- Wish
- Protect
- Toxic
- Aromatherapy / Draining Kiss
Bleh normal bulky kind of set with a Pokemon who has bad stats. Wish/Protect for recovery and if neccesary team healing, though meh HP, Toxic is to deal meaningful damage and Aromatherapy to screw status or Draining Kiss to prevent taunt fodder. Sweet Veil protects the team from sleep, and the EVs are to give Slurpuff some chance of surviving a physical attack. At least it checks fighting types and stuff. :D!

Desserts try rebel
Slurpuff @ Lum Berry / Luminous Moss / Weakness Policy /any item that can be consumed and be helpful to Slurpuff :D
Trait: Unburden
EVs: 252 HP / 180 Def / 72 S. Def / 4 Spe
- Cotton Guard / Aromatherapy
- Calm Mind
- Wish
- Draining Kiss / Dazzling Gleam
Ehh. Anyway, gimmick sweeper that could work I suppose. Using a consumable item, not sure (If you want to follow what people say on youtube, run Luminous Moss and pair it with Greninja in doubles apparently) what, but once it's consumed Slurpuff gets the unburden boost, and with 4 Spe EVs gets a 362 speed, outspeeding base 115s for no reason in particular by 1 point. Full EVs are dumped onto HP to maximise bulk and the rest are carelessly thrown between Def and SDef. Cotton Guard increases defense, while Aromatherapy functions as a status remover, which is the best thing to take down Slurpuff especially if it's set up really. Calm Mind is to boost special defense, while Wish heals and Draining Kiss is the attack move, which also heals. Or Dazzling Gleam for stronger STAB.

Now I will post my more powerful Slurpuff, the Special Sweeper.
Slurpuff
Ability: Sweet Veil
Item: Pixie Plate
Draining Kiss
Energy Ball
Flamethrower
Surf
This set has amazing coverage for I believe 10 or 11 types. The types of Fairy, and the classic starter types has few that will resist. Draining Kiss is STAB with reliable recovery. Energy Ball got buffed to the same power as the classic Tbolt, Fthrower and Ice Beam and has a chance to lower Sp. Def, which is good for this set. Flamethrower has good power with a chance to burn, which is good for wearing things down. Surf has coverage against Fire types which resist its other three attacks so it doesn't get walled by fire types like Torkoal or Delphox. I love this set and Pokemon, so I hope this helps.

Belly Drum + Sitrus Berry + Unburden combo is self explanatory. Play Rough is STAB, Return hits Poison-types neutrally, and Thief hits Steel-types and can give you a new item like Leftovers or even a new item to activate Unburden and get another Speed boost.

Dazzling Gleam is STAB that takes care of Dragons who resist your other moves. Flamethrower covers that Steel-type weakness, and can help against a Dry Skin Toxicroak. Surf & Thunderbolt provide good coverage with the other moves.